It’s been fun to talk with people suffering from Delayed Sleep Phase over the last couple days. There’s been some questions about shifting sleep phase using light therapy and melatonin supplements. The timing of these therapies depends on whether you want to delay sleep, ie. make it begin later, or advance sleep, making it occur earlier. Once you know that, then you use the Phase Response Curve to see when to use these therapies.
A word of warning: The correct timing is crucial, so it is best to work with a sleep professional if you want to shift your sleep phase. If you use light or melatonin therapy at the wrong time you can cause problems by shifting your circadian rhythm the wrong direction.
Follow this link to the Phase Response Curve on Wikipedia: http://en.wikipedia.org/wiki/File:PRC-Light%2BMel.png
On the horizontal axis you see time, and the sleep period written in. On the vertical axis you see hours of phase advance on the top, and hours of phase delay on the bottom. Bright light is represented by dark purple, melatonin by green. Note that the light curve goes both higher and lower than the melatonin, that is because a much larger phase shift can be achieved with light.
Let’s look at an example. Say an adult is unable to sleep until 2am, but must get up for work at 7am. Getting 5 hours of sleep each night is not enought for her. She would like to sleep from 11pm to 7am, but is just not sleepy. Using the Phase Response Curve, she begins using light therapy each morning when she gets up for the day. She also takes some melatonin 6 hours before bed. These combined therapies allow her to feel sleepy at 11pm, and fall to sleep easily. Now she can get a full night’s sleep, and all the benefits of sufficient sleep.